While blooms the size of dinner plates aren’t unusual for hibiscus (Hibiscus spp.), tiny black aphids prefer meals served off the plants’ unopened buds. Endlessly annoying and perpetually pregnant, cotton aphids strike in temperate areas of hibiscus’ growing range in U.S. Department of Agriculture plant hardiness zones 2a through 11b. Sap loss from prolonged aphid attacks stunts and weakens hibiscus. Managing the pests, also known as melon aphids, is relatively simple and inexpensive.
A Bug of Many Colors
The aphids invading your hibiscus’ buds are either winged males that appear only in fall, or winged females that have migrated in from overcrowded or declining plants to mate and lay their eggs. Although these forms of the 1/16-inch pests appear black to the naked eye, they’re actually greenish-black with black legs and thoraxes. Non-migrating females and aphid nymphs may be yellow, blue-green or grayish-black.
Adult female aphids live three to four weeks and give birth to up to 85 live female nymphs, each of which begins producing live offspring within four days to a week. In warm, Mediterranean-style climates, this reproductive extravaganza may continue all year. The resulting population explosion could easily decimate your hibiscus and drench it in their sticky waste. With the help of beneficial insects that prey on the pests, reducing their colonies to harmless numbers is within your reach.
Turn the Ladies Loose
A single commercially available, red and black convergent ladybug lays up to 1,000 eggs over the spring and summer. In the process, she eats up to 50 aphids each day. Compared to the 4,000 to 9,000 each of her babies gobbles up, that’s a starvation diet. Two releases of 1,500 convergent ladybugs spaced a week apart should be enough to control the aphids on a large, heavily infested hibiscus. Mist the plant well and turn the bugs loose after dark, placing them on the soil around its base or on the lowest branch crotches.
Water or Soap
If your area isn’t under drought restrictions, try dislodging small aphid colonies from your hibiscus with a strong water spray. Manage larger ones by spraying the plants on a cloudy day with ready-to-use insecticidal soap until all their surfaces drip, and repeat every two to three days, or the label’s specified interval, until their predators manage the pests. To avoid injuring foraging honeybees, spray early in the day or after dark. Dress in a washable, long-sleeved shirt, long pants, and hat and use protective eyewear while using the soap.
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